Update: The date for this change has moved to February 25, 2019.
What's changed?
There are three major changes being announced in this post:
Aggregated product statistics in Accountstatuses
The number of products in a given account can now be retrieved directly from 
Accountstatuses. Like the Merchant Center, you can retrieve the following aggregated statistics: active products, expiring products, disapproved products, and pending products. These statistics are given separately for each combination of destination, channel, and target country. For example:
"products": [{
  "country": "US",
  "destination": "Shopping",
  "channel": "online",
  "statistics": {
    "active": "1542",
    "expiring": "14",
    "disapproved": "152",
    "pending": "743"
  },
  ...
}]
Here, there are 1542 active products that target the USA that can be used in online Shopping campaigns, 14 active but expiring products, 152 disapproved products, and 743 pending products.
Product-level issues in Accountstatuses
In addition to the new product statistics, the "products" field also contains an 
itemLevelIssues field similar to 
the itemLevelIssues field added to 
Productstatuses earlier this year. Using the contents of this field, you can now see explicitly whether a given issue is impacting the servability of a product and whether the issue needs your attention or just further processing on Google's part.
Human-readable descriptions in itemLevelIssues
In both 
Productstatuses and 
Accountstatuses, the objects in the 
itemLevelIssues field now have some additional fields, which contain English descriptions and helpful links for issues that are suitable for surfacing to clients. The following fields have been added:
  - descriptioncontains a short English description of the issue.
- detailcontains a detailed English description of the issue.
- documentationcontains a URL for a web page that can help resolve the issue.
Here is an example 
itemLevelIssues object that includes these fields:
{
  "attributeName": "image link",
  "code": "image_link_pending_crawl",
  "description": "Image not retrieved (crawl pending)",
  "destination": "Shopping",
  "detail": "Wait for the product image to be crawled (up to 3 days)",
  "documentation": "https://support.google.com/merchants/answer/160640",
  "resolution": "pending_processing",
  "servability": "disapproved"
}
What do you need to do?
Now that the human-readable information is available for 
itemLevelIssues in both systems, we now consider the old 
dataQualityIssues fields deprecated. We will no longer include them in 
Productstatus or 
Accountstatus resources on 
Dec 1, 2018, therefore you should migrate to the new 
itemLevelIssues fields as soon as possible.
If you have any questions or feedback about this change, or any other questions about the Content API for Shopping, please let us know on the 
forum.
 - Stevie Strickland, Content API for Shopping Team